In recent years, a projection display apparatus using various light modulation elements has attracted attention as a projection video apparatus of providing large-screen display.
In the large-screen display provided by using the projection display apparatus, it is required to secure sufficient brightness of an image determined by luminance of a lamp, optical collection efficiency of a concave mirror, lighting efficiency of a lighting lens system, optical usable efficiency of the light modulation elements and so on.
Here, conventional light source apparatuses will be specifically described.
(1) To begin with, configuration and operation of a conventional light source apparatus (1) will be described with reference to FIG. 14 which is a schematic sectional view thereof (refer to the specification of Japanese Patent No. 3151734 for instance).
The disclosure of the specification of Japanese Patent No. 3151734 is incorporated herein by reference in its entirety.
The conventional light source apparatus (1) comprises a first concave mirror M11 formed using an ellipsoidal mirror (or a parabolic mirror) and a second concave mirror M12 formed using a spherical mirror.
The first concave mirror M11 and second concave mirror M12 are placed so that their apertures face each other and their focuses are approximately matching.
Of course, a light emitting portion of a lamp L10 is placed at positions of these focuses.
The conventional light source apparatus (1) has the second concave mirror M12 placed on a different side from a vertex V10 of the first concave mirror M11 with respect to the light emitting portion of the lamp L10.
On the conventional light source apparatus (1), the aperture of the second concave mirror M12 is perpendicular to an optical axis (shown in dashed line, same hereafter), and an outermost diameter perpendicular to the optical axis of the second concave mirror M12 is larger than the outermost diameter of the first concave mirror M11.
Luminous flux (shown in chain double-dashed line, same hereafter) emitted from the light emitting portion of the lamp L10 is focused by the first concave mirror M11.
However, the luminous flux which could not be directly focused just by the first concave mirror M11 is reflected once on the second concave mirror M12 of which reflecting surface is facing the reflecting surface side of the first concave mirror M11 and returned again to the vicinity of the light emitting portion of the lamp L10 before focused by the first concave mirror M11.
For this reason, the conventional light source apparatus (1) can focus the luminous flux which could not be focused just by the first concave mirror M11 by using the second concave mirror M12 so as to improve the optical collection efficiency which is important for the sake of maximizing the luminance of the lamp L10.
(2) Next, the configuration and operation of a conventional light source apparatus (2) will be described with reference to FIG. 15 which is a schematic sectional view thereof (refer to the specification of Japanese Patent No. 2730782 and Japanese Patent Laid-Open No. 11-162219 for instance).
The disclosure of the specification of Japanese Patent No. 2730782 and Japanese Patent Laid-Open No. 11-162219 is incorporated herein by reference in its entirety.
On the conventional light source apparatus (2), the luminous flux which could not be directly focused just by the first concave mirror M21 is reflected once on the second concave mirror M22 and returned again to the vicinity of the light emitting portion of the lamp L20 before focused by the first concave mirror M21.
On the conventional light source apparatus (2), however, the aperture of the second concave mirror M22 is parallel to the optical axis, and the outermost diameter perpendicular to the optical axis of the second concave mirror M22 is smaller than the outermost diameter of the first concave mirror M21.
For this reason, the conventional light source apparatus (2) can have a smaller apparatus configuration than that of the above-mentioned conventional light source apparatus (1).
(3) Next, the configuration and operation of a conventional light source apparatus (3) will be described with reference to FIG. 16 which is a schematic sectional view thereof (refer to the specification of U.S. Pat. No. 4,305,099, Japanese Patent Publication No. 7-107596 and Japanese Patent Laid-Open No. 2002-367417 for instance).
The disclosure of the specification of U.S. Pat. No. 4,305,099, Japanese Patent Publication No. 7-107596 and Japanese Patent Laid-Open No. 2002-367417 is incorporated herein by reference in its entirety.
On the conventional light source apparatus (3), the luminous flux which could not be directly focused just by the first concave mirror M31 is reflected once on the second concave mirror M32 and returned again to the vicinity of the light emitting portion of the lamp L30 before focused by the first concave mirror M31.
However, the conventional light source apparatus (3) has the second concave mirror M32 placed, with respect to the light emitting portion of the lamp L30, on the same side as a (virtual) vertex V30 of the first concave mirror M31 and farther from the light emitting portion of the lamp L30.
The conventional light source apparatus (3) has the lamp L30 placed so that a longitudinal direction of electrodes of the lamp L30 becomes orthogonal to an optical axis direction.
For this reason, the conventional light source apparatus (3) comprises a parallel light converting portion having a positive lens (convex lens) PL and a negative lens (concave lens) NL to use the luminous flux in the optical axis direction more effectively.
(1) In the above-mentioned conventional light source apparatus (1), there are the cases where it has a negative effect of extending a spot diameter of an optical spot formed on a focusing point as regards the luminous flux emitted from the light emitting portion of the lamp L10 and reflected on a point of reflection in the vicinity of the vertex V10 of the first concave mirror M11.
Analysis by the Inventors
According to an analysis by the inventors, this is because the light emitting portion of the lamp L10 is not a point source but is a light source having a size, and regarding the luminous flux reflected on the point of reflection in the vicinity of the vertex V10 of the first concave mirror M11, an optical path distance from the light emitting portion of the lamp L10 to the point of reflection thereof becomes significantly shorter than the optical path distance from the point of reflection to the focusing point.
(2) For the same reason, there are also the cases where the above-mentioned conventional light source apparatus (2) has the negative effect of extending the spot diameter of the optical spot formed on the focusing point as to the above-mentioned luminous flux.
(3) The above-mentioned conventional light source apparatus (3) seldom has such a negative effect.
According to the analysis by the inventors, this is because the optical path distance from the light emitting portion of the lamp L30 to the point of reflection thereof does not become too short compared to the optical path distance from the point of reflection to the focusing point (as the second concave mirror M32 is placed, with respect to the light emitting portion of the lamp L30, on the same side as the vertex V30 of the first concave mirror M31 and farther from the light emitting portion of the lamp L30, an optical path going through the point of reflection of the second concave mirror M32 is generated as to the luminous flux which should originally be reflected on the point of reflection in the vicinity of the vertex V30 of the first concave mirror so as to extend the optical path distance from the light emitting portion of the lamp L30 to the point of reflection of the first concave mirror M31).
However, the inventors noted that there are the cases where the above-mentioned conventional light source apparatus (3) cannot obtain a sufficient usable amount of light of the light passing through the aperture of the first concave mirror M31.
The inventors analyze the reason as follows.
To be more specific, in the case of the above-mentioned conventional light source apparatus (3), the luminous flux which should originally be reflected on the point of reflection rather far from the vertex V30 of the first concave mirror M31 near the light emitting portion of the lamp L30 is reflected once on the second concave mirror M32 and returned to the vicinity of the light emitting portion of the lamp L30 again before focused by the first concave mirror M31.
When reflected once on the second concave mirror M32, efficiency of the luminous flux is reduced due to a reflectance of the reflecting surface thereof.
The efficiency of the luminous flux is also reduced due to light absorption and light scattering by a light-emitting material of the lamp L30 and a material comprising the lamp L30 when returned to the vicinity of the light emitting portion of the lamp L30. In the case where the lamp L30 is a metal halide lamp or a mercury lamp, the efficiency of the luminous flux is reduced by as much as 60 percent or so when returned to the vicinity of the light emitting portion of the lamp L30, which is particularly conspicuous.
In short, the inventors noted that there are the cases where the efficiency of the luminous flux emitted from the light-emitting portion of the lamp L30 is reduced because the luminous flux which can be directly focused by the first concave mirror M31 is focused through reflection by the second concave mirror M32.